Part of the async i/o solution for Guile involves "prompts" (more formally delimited continuations) that allow defining new types of control flow operators. He

Part of the async i/o solution for Guile involves "prompts" (more formally delimited continuations) that allow defining new types of control flow operators. Here's a simple cooperative multitasking implementation and a contrived example program that uses it: ;; Core implemenation (define (call-with-coroutine thunk) "Apply THUNK with a coroutine prompt." (define (handler cont callback . args) (define (resume . args) ;; Call continuation that resumes the procedure. (call-with-prompt 'coroutine-prompt (lambda () (apply cont args)) handler)) (when (procedure? callback) (apply callback resume args))) ;; Call procedure. (call-with-prompt 'coroutine-prompt thunk handler)) (define (yield callback) "Yield continuation to a CALLBACK procedure." (abort-to-prompt 'coroutine-prompt callback)) ;; Simplistic example (define *cont* #f) (define (pause) (yield (lambda (cont) (set! *cont* cont)))) (define (resume) (*cont*)) ;; Prints "foo" (call-with-coroutine (lambda () (display "foo\n") (pause) (display "bar\n") (pause) (display "baz\n"))) (resume) ; prints "bar" (resume) ; prints "baz"